1. Field of the Invention
This invention relates to primer compositions, and more particularly to very useful primer compositions as a primer to be applied to the coated surface of adherends on which a coating film is formed by applying an acrylic resin electrodeposition-coating, a fluororesin coating or the like to various adherends, when adhering a condensation type room temperature curable silicone rubber to said adherends having the coating film.
2. Description of the Prior Art
Silicone rubbers are broadly used as construction sealants, industrial adhesive sealing materials, electrical insulating materials, and potting materials, because they are excellent in heat resistance, cold resistance, ultraviolet resistance etc. and generally have also excellent electrical properties. However, among these silicone rubbers, some condensation type room temperature curable silicone rubbers do not exhibit adhesion properties to various adherends, so that these adherends should be previously treated with a primer. Some condensation curable type silicone rubbers of another type show adhesion properties per se to various adherends but the adhesion properties are not sufficient to ensure a permanent adhesion as required for said uses, so that the treatment with a primer is also required as in the above.
As primer compositions for silicone rubbers, which are curable at room temperature by condensation, there have hitherto been known so-called silane coupling agents and their reaction products, mixtures of polyisocyanates and chlorinated rubbers, mixtures of polyester resins and acrylic resins, and mixtures of phenyl-radical containing siloxanes, alkyl silicates and chlorosilanes, and the like.
While, as outer walls for construction, there have been extensively used in recent years those having a coating film which is formed by applying a fluororesin-based coating, an acrylic resin-based coating or the like to the surface of the wall, said coatings having properties excellent in weather resistance, chemical resistance, electrical insulation, inflammability and the like. However, the condensation type room temperature curable silicone rubbers as mentioned above do not exhibit a good adhesion to such a coating film, and there occurred a problem that even if using a primer containing, as the base component, conventionally known silanes or their cohydrolytic condensation products, i.e., silicone resins, the adhesion properties can not be improved.